Electric machine fault detection scheme
A short circuit detection system and method that identifies a short circuit between turns of a winding of a permanent magnet machine having a three-phase winding in response to detection of imbalances between the three motor phases at an instant in time. The imbalances are identified by monitoring motor terminal voltages and currents.
1. A method of detecting an inter-turn short-circuit in a winding of a multiple phase motor, being a multiple winding permanent magnet machine, the method comprising:
detecting an imbalance between current and/or voltage of winding of a multiple phase motor, being a multiple winding permanent magnet machine; and
determining a short-circuit in a winding of the machine based on detection of the imbalance;
wherein at zero to medium motor speeds, the imbalance is detected by injecting a high frequency signal into a signal provided to drive the motor and determining a short-circuit is based on an imbalance in a feedback signal from the motor; and
wherein at higher motor speeds determining a short-circuit based on the signal to drive the motor.
2. The method of claim 1 , wherein the imbalance is detected in drive signals provided to the permanent magnet machine terminals at higher motor speeds.
3. The method of claim 1 , wherein the imbalance is detected in feedback signals from the permanent magnet machine at zero to medium motor speeds.
4. The method of claim 1 , wherein the high frequency signal is injected into command voltages in an alpha-beta frame.
5. The method of claim 1 , wherein the high frequency signal is injected into voltages in a dq frame.
6. The method of claim 1 , wherein the high frequency signal is injected directly into phase voltages at the motor terminals.
7. The method of claim 1 , wherein a short-circuit is determined using a processing function comprising an absolute function, a low pass filter and a window comparator to determine whether all phase signals are within a given band, wherein if signals are outside the band, a short-circuit is determined.
8. The method of claim 1 , wherein on determination of a short circuit in a winding, the winding is deactivated from operation of the permanent magnet machine.